Molded waveguide and method for making same

ABSTRACT

A method for manufacturing a molded waveguide (50) is provided. A first cladding layer (20) is provided. Channels (21) are formed in the first cladding layer (20). A second cladding layer (40) is subsequently provided. The channels (21) in the first cladding layer (20) are then filled with an optically transparent polymer. The second cladding layer (40) is subsequently affixed over the channels (21) of the first cladding layer (20), thereby enclosing the channels (21).

This is a division of application Ser. No. 07/889,335, filed May 28,1992 now U.S. Pat. No. 5,265,184 issued Nov. 23, 1993.

BACKGROUND OF THE INVENTION

This invention relates, in general, to waveguides and, moreparticularly, to fabrication of molded waveguides.

At the present time, fabrication of optical waveguides is achieved byeither a polymer spin-on technique or a diffusion technique, both ofwhich require expensive photolithography steps. Additionally, bothfabrication techniques are ineffective and inefficient for fabricatingoptical waveguides in high volumes for several reasons, such as complexprocessing steps, difficulties in controlling the processing steps, andhigh cost.

Briefly, as practiced by one method in the prior art, a polymeric filmis spun onto a substrate. Portions of the polymeric film aresubsequently exposed to light by a photolithographic process, therebychanging the refractive index of the polymeric film and creating awaveguide in the polymeric film. However, subsequent multi-stepprocessing, such as removal of the polymeric film from the substrate,lamination processing, curing, and other processes typically arerequired for the waveguide to be useful. Further, it should be notedthat each additional processing step incurs an additional cost, as wellas presenting an opportunity to induce defects into the waveguide.

Alternatively, in another method practiced in the prior art, a layersuch as a glass is applied to a substrate. The layer is patterned by acomplicated photolithography process, thereby producing portions thatare masked and portions that are open or clear. Typically, ions aresubsequently diffused into the open portions of the layer, thus changingthe refractive index of the layer and making a waveguide. However, byusing a photolithography process, a high cost is incurred intomanufacturing of the waveguide. Also, by using diffusion processes tochange the refractive index of the layer, control of dimensionality ofthe waveguide is severely limited.

Additionally, while making grooves in a plastic material andsubsequently filling of these grooves with material for conducting lighthas been done in the past, these methods are only adequate for largemechanical orientated optical systems. Further, these methodscharacteristically are inefficient at conducting light, thus making themunsuitable for use in high speed communications.

It can be readily seen that conventional methods for making waveguideshave severe limitations. Also, it is evident that the conventionalprocessing uses a multitude of steps which are not only complex andexpensive, but also not effective processing. Therefore, a method formaking a waveguide that provides a reduction in the number of stepsrequired, reduces cost, and simplifies the processes necessary formaking a waveguide would be highly desirable.

SUMMARY OF THE INVENTION

Briefly stated, a method for manufacturing a molded waveguide isprovided. A first cladding layer is provided. Channels are formed in thefirst cladding layer. A second cladding layer is subsequently provided.The channels in the first cladding layer are then filled with anoptically transparent polymer. The second cladding layer is subsequentlyaffixed over the channels of the first cladding layer, thereby enclosingthe channels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified cross-sectional view of a mold;

FIG. 2 is a simplified cross-sectional view of a molded first claddinglayer;

FIG. 3 is a simplified cross-sectional view of another mold;

FIG. 4 is a simplified cross-sectional view of a molded second claddinglayer;

FIG. 5 is a simplified cross-sectional view of the molded first claddinglayer and the molded second cladding layer affixed together; and

FIG. 6 is a partially exploded simplified pictorial view of an opticalelectronic module.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified cross-sectional view of a mold 10 used for makinga first cladding layer 20 shown in FIG. 2. It should be understood thatmold 10 has been greatly simplified and that only a brief description ofmold 10 is necessary for a clear understanding of the present invention.Typically, mold 10 is made of a top portion 11 and a bottom portion 12.Commonly, these top and bottom portions, 11 and 12, are made of a metalmaterials, such as stainless steel, aluminum, or the like. Further,these top and bottom portions 11 and 12 typically are configured so asto provide appropriate heating and cooling capabilities, as well asproviding necessary pressure capabilities that are dictated by theselection of the molding materials or molding compounds. Template 13typically is made of similar materials as are top and bottom portions 11and 12. However, it should be understood that while template 13 isadvantageous for manufacturing small volumes of a molded product,template 13 would be incorporated into bottom portion 12 for use inmanufacturing high volumes of a molded product.

Generally, with template 13 placed in bottom portion 12, with topportion 11 and bottom portion 12 securely held together, with theappropriate process conditions selected for the specific moldingcompound or molding material, the molding material is injected intocavity 16, represented by arrow 14. Features 19 of template 13 are madein a variety of cross-sectional shapes and sizes, such as V-grooves,semicircles, U-grooves, rectangular grooves, with a minimum feature sizeof 0.5 micron or the like. Further, it should be understood thatfeatures 19 extend longitudinally into the paper and that many differentgeometric patterns are capable of being fabricated with features 19 ,such as bending or curving of features 19, joining or splitting offeatures 19, or the like as illustrated in FIG. 6. Also, width 15 offeatures 19 is capable of being adjusted to meet specific designrequirements, such as optical mode mixing, optical mode matching, oradiabatic tapering. However, in a preferred embodiment of the presentinvention, a rectangular groove that is 50.0 microns by 50.0 microns oneach side is used.

Typically, the molding compound is made of an optically transparentmaterial, such as epoxies, plastics, polyimides, or the like. Generally,refractive indexes of these optically transparent materials range from1.50 to 1.54. In a preferred embodiment of the present invention,optically transparent epoxies are used as the molding material.Processing conditions for these materials range from 22 degrees Celsiusto 200 degrees Celsius for molding temperatures and 200 pounds persquare inch to 2,000 pounds per square inch for molding pressures. Byinjecting the molding material, represented by arrow 14, into cavity 16,intricacies of surface 17 of template 13 and intricacies of surface 18of upper portion 11 are transferred to the molding compound. Asubsequent curing process solidifies the molding compound, therebypermanently transferring the intricacies or a negative image of surfaces17 and 18 to the solidified molding compound in cavity 16.

Once the curing processes are completed, mold 10 is opened and a moldedfirst cladding layer 20, as shown in FIG. 2, is removed from mold 10.

FIG. 2 is a simplified cross-sectional view of the molded first claddinglayer 20 formed as described with reference to FIG. 1. Typically,channels 21 are made as rectangular grooves; however, other geometricconfigurations may be made, such as U-grooves, semicircles, V-grooves,or the like. In addition, channels 21 and 22 are made in such a mannerso as to produce smooth defect free surfaces. Surfaces 24 and surface 26may also be smooth and defect free; however, these surfaces may also beshaped according to specific application. For example, surface 26 may bemodeled to provide a greater surface area. Also, it should be understoodby one skilled in the art that by molding channels 21 a smooth defectfree surface is achieved at a minimal cost. Typically, surface 22 offirst cladding layer 20 is recessed into first cladding layer 20,thereby allowing a subsequent adhesive to be spread into channels 21 andacross surface 22 without significantly entering openings 23.

FIG. 3 is a simplified illustration of a cross-sectional view of a mold30 used for making a second cladding layer 40 as shown in FIG. 4.Typically, mold 30 is made of an upper portion 31, a lower portion 32,and a template 33. However, while template 33 is advantageous for lowvolume manufacturing, it should be realized by one skilled in the artthat template 33 would be incorporated into bottom portion 32 in highvolume manufacturing.

Generally, as described with reference to FIG. 1 regarding mold 10, mold30 is closed and brought to appropriate processing conditions. Themolding material is injected into cavity 36, represented by arrow 34,thus filling cavity 36. By filling cavity 36 with the molding compound,surfaces 37 and 38 are replicated by the molding compound. Also, aspreviously describe with reference to FIG. 1, molding compound 34 iscured, solidified, and subsequently removed from mold 30, therebyproviding second cladding layer 40 as shown in FIG. 4. Further, whilemold 10 and mold 30 are discussed separately hereinabove, it should beunderstood that mold 10 and mold 30 typically are made together as partof a whole larger mold (not shown). By making mold 10 and mold 30together several advantages are realized, such as facilitating roboticremoval and subsequent robotic processing of first cladding layer 20 andsecond cladding layer 40, injection of the molding compound can be thesame, thus producing similar or equal refractive indexes in firstcladding layer 20 and second cladding layer 40.

FIG. 4 is a simplified cross-sectional view of molded second claddinglayer 40 formed as with reference to FIG. 3. Typically, second claddinglayer 40 is made in such a manner that surface 41 of second claddinglayer 40 fits snugly against surface 22 of first cladding layer 20, asshown in FIG. 5. Additionally, a surface 42 may be modeled to suitspecific applications, such as increasing surface area.

FIG. 5 is a simplified cross-sectional view of a molded waveguide 50.Molded waveguide 50 is made of first cladding layer 20, second claddinglayer 40, and core material 52. It should be evident that first claddinglayer 20 has been inverted so as to facilitate the viewing of moldedwaveguide 50.

Typically, molded first cladding layer 20 and molded second claddinglayer 40 are joined by an optically transparent material which forms thecore of the waveguide and acts as an adhesive or an opticallytransparent polymer. The optically transparent adhesive generally may beany of several materials, such as epoxies, plastics, polyimides, or thelike. Generally, refractive indexes of these optically transparentmaterials range from 1.54 to 1.58. It should be understood that to forman optical waveguide the refractive index of core 52 must be at least0.01 greater than that refractive index of cladding layers 20 and 40.However, in a preferred embodiment of the present invention, epoxies areused to join first cladding layer 20 to second cladding layer 40.Application of the adhesive is done in such a manner so as to completelyfill channels 21 of first cladding layer 20, thereby forming core 52.Further, by having core 52 completely surrounded by cladding layers 20and 40, core 52 has superior performance characteristics for conductinglight or light signals. These superior performance characteristics areused in enhancing high speed communications applications, such aschip-to-chip communications, board-to-chip communications,board-to-board communications, computer-to-computer communications, andthe like. Additionally, a capability is available, in the presentinvention, to match refractive indexes of cladding layers 20 and 40.However, while the adhesive completely fills channels 21 of firstcladding layer 20, the adhesive is restricted from alignment ferrules 51by slightly inclining a surface 53. Alignment ferrules 51, as shown inFIG. 5, are made by adhering first cladding layer 20 and second claddinglayer 40 together; however, it should be evident to one skilled in theart that alignment ferrules 51 may be made by inverting openings 23 asshown in FIG. 2 into second cladding layer 40. It should be understood,however, that inverting openings 23 as shown in FIG. 2 into secondcladding layer 40 can degrade alignment of alignment ferrules 51 to core52. Typically, the adhesive is cured by a variety of methods, such asair drying, exposure to UV light, heat treating, or the like. Selectionof specific curing methods is application specific as well as beingdependent upon selection of adhesive and cladding materials that areused for making first and second cladding layers 20 and 40.

By way of example only, first cladding layer 20 and second claddinglayer 40 are made by injecting a transparent epoxy molding compound,available under the Tradename HYSOL MG18 from Dexter Corporation, intomolds 10 and 30, respectively. Temperature of molds 10 and 30 rangebetween 150° C. to 175° C. with a preferred temperature range from 160degrees Celsius to 165 degrees Celsius. Molding pressure of molds 10 and30 range between 500 psi to 1,000 psi with a preferred pressure rangefrom 750 pounds per square inch to 800 pounds per square inch.Typically, transfer time ranges from 30 to 50 seconds at a temperatureof 150° C. to 20 to 30 seconds at a temperature of 175° C. Curing timetypically ranges from 3 to 5 minutes at 150° C. to 2 to 4 minutes at atemperature of 175° C. Upon completion of the curing time, firstcladding layer 20 and second cladding layer 40 are removed from molds 10and 30, respectively. Typically, a post-curing step is necessary inorder to achieve maximum physical and electrical properties of the HYSOLmaterial. This step generally proceeds at 150 degrees Celsius forapproximately 2 to 4 hours. Completion of the post-cure step results infirst cladding layer 20 and second cladding layer 40 having a refractiveindex of approximately 1.52.

Once the molding and curing processes, as well as the removal of thefirst and second cladding layers 20 and 40 from their respective moldshave been completed, the first and second cladding layers 20 and 40 areready to be assembled. Assembly of the first and second cladding layers20 and 40 is achieved by applying an optically clear adhesive with arefractive index at least 0.01 higher than the first and second claddinglayers 20 and 40 to surface 22. In a preferred embodiment of the presentinvention, these requirements are fulfilled by applying an opticallyclear epoxy available under a Tradename EPO-TEK 301-2 from EPOXYTECHNOLOGY INC. Typically, after the adhesive is applied to surface 22of the first cladding layer 20, surface 41 of second cladding layer 40is compressed against surface 22 of first cladding layer 20, therebysqueezing and filling channels 21 and adhering both first cladding layer20 and second cladding layer 40 together. Additionally, it should beunderstood that by adhering first cladding layer 20 and second claddinglayer 40 together, alignment ferrules 51 are formed. Curing times forthe adhesive epoxy is dependent upon temperature, e.g., at roomtemperature curing time is 2 days and at 80 degrees Celsius curing timeis 1.5 hours.

FIG. 6 is a simplified partially exploded pictorial view of an opticalelectronic module 60. In the present invention molded optical waveguide61 is electrically coupled to standard electronic components.

Typically, waveguide 61 is fitted with optical components, such as aphototransmitter or laser 62, a photodetector or photodiode 63, or acombination of both lasers and photodetectors. Alternatively, an array64 can be mounted on waveguide 61 which contains a variety of opticalcomponents. The optical components are mounted to molded opticalwaveguide 61 in such a manner that individual working portions of theoptical components are aligned to an individual waveguide, thusproviding maximum light transmission through individual waveguides. Forexample, laser 62 is mounted to tab 67 and tab 68 by solder bump 69. Byaccurately placing and solder bumping laser 62 to molded opticalwaveguide 61, light transmission from the working portions of laser 62through waveguide 71 is maximized.

Generally, molded optical waveguide 61 with attached optical componentsis attached to interconnect board 66. Several methods may be used forattaching interconnect board 66 to molded optical waveguide 61, such asadhering, press fitting, molding or the like. However, in a preferredembodiment of the present invention, an epoxy adhesive is applied tointerconnect board at an approximate location where the molded opticalwaveguide 61 and the interconnect board 66 are to be bonded. Waveguide61 is placed onto the adhesive by an automated system such as a robotarm, thereby providing accurate placement and orientation of waveguide61.

Subsequent electrical coupling of standard electrical components, asillustrated by integrated circuit 74, on interconnect board 66 to theoptical components is achieved by a wire bond 76 from bonding pad 77 totab 67. It should be evident by one skilled in the art, that many moreelectrical couplings typically are necessary to fully utilize inputs andoutputs of both the standard electrical components and the opticalcomponents. It should be further evident that standard output and inputmeans, represented by lead 78, are used to couple other components aswell.

Further, plastic encapsulation of interconnect board 66 and moldedoptical waveguide 61 typically is achieved by an over-molding process,represented by plastic pieces 79, which encapsulates interconnect board66 and optical waveguide 61 while leaving alignment ferrules 81 open andclear of debris. Alignment ferrules 81 are then engaged by alignmentpins 84 of optical fiber ribbon 85, thereby providing accurate andrepeatable alignment of waveguides 71, 72, and 73 to optical fiberribbon 85.

By now it should be appreciated that a novel method for making a moldedoptical waveguide and an optical electrical module have been described.The method allows for the making of waveguides cost effectively, thusallowing their usage in optical electrical modules. Additionally, thismethod allows for an inexpensive process for combining both standardelectrical components and optical components.

We claim:
 1. A molded waveguide comprising:a first molded cladding layerhaving a plurality of channels with some of the plurality of channelshaving adiabatic tapering; a second molded cladding layer; and anadhesive core material, wherein the adhesive core material fills theplurality of channels securing and covering the plurality of channels ofthe first molded cladding layer with the second molded cladding layer,thereby making a molded waveguide; an alignment guide placed on thecladding region of the molded waveguide for alignment of an opticalconnector.
 2. A molded split waveguide comprising:a first cladding layerhaving an adiabatic configured channel; a second cladding layer affixedto the first cladding layer with an optically transparent polymer thatforms a core region add fills the adiabatic configured channel, therebymaking a molded split waveguide: and an alignment guide placed on thecladding region of the molded split waveguide for alignment of anoptical connector.
 3. An adiabatic molded waveguide comprising:a firstmolded cladding layer having a first end, and a second end; a pluralityof channels with some of the plurality of channels extending from thefirst end of the first molded cladding layer to the second end of thefirst molded cladding layer and with some of the plurality of channelshaving adiabatic tapering at the first end of the first molded claddinglayer; a second molded cladding layer; and an adhesive core material,wherein the adhesive core material fills the plurality of channelssecuring and covering the plurality of channels of the first moldedcladding layer with the second molded cladding layer, thereby making anadiabatic molded waveguide.
 4. An adiabatic tapered waveguide as claimedin claim 3 further including an alignment guide located on the firstcladding layer of the adiabatic molded waveguide.